This invention relates generally to medical devices and, in particular, to an indwelling valved prosthesis.
Anti-reflux esophageal prosthesis or stents are typically placed in the lower esophagus and through the lower esophageal sphincter to maintain the patency thereof due to the presence of a cancerous tumor commonly found in the vicinity thereof. The cancerous tumor growth typically impinges the flow of food and fluids through the esophagus. Lower esophageal cancer in the United States presently occurs at the rate of approximately 12,000 patients per year. The incidence in the United States is approximately 5.1 per 100,000 people, which is rising particularly in white male patients. Esophageal prosthesis or stents are typically utilized in these cancerous patients. However, these devices are not FDA approved for benign tumors which also cause blockage or partial stenosis of the esophagus. Esophageal prosthesis or stents are utilized in Europe and other countries for benign tumor conditions, but not in the United States at this time.
A problem with esophageal prosthesis or stents is that fluid from the stomach flows into the mouth of the patient when in a prone position. In an attempt to solve this problem, a number of esophageal prosthesis or stents utilize a one-way valve such as a duck-bill or reed-type valve in which only food or fluid from the esophagus flows into the stomach in only an antegrade or forward direction. However, these one-way anti-reflux prosthesis or stents present another problem. When the patient wants to belch or vomit, he/she is prevented from doing so, because the one-way valve prevents backward flow in the retrograde direction. Such condition is not only painful to the patient, but can also lead to more complicated medical conditions.
There are other anatomical sites, such as the biliary tree or genitourinary system in which a prosthesis may be placed to maintain an open lumen for passage of bodily fluids, thereby creating risk of undesirable retrograde flow and/or migration of pathogenic organisms which could lead to infection or other problems, such as obstruction of the stent. When a drainage stent or catheter is placed across a sphincter or natural stricture at the opening to a bodily passage, the sphincter or stricture cannot fulfill its normal function of restricting retrograde flow or migration. What is needed is a prosthesis and one-way valve that can effectively regulate antegrade and retrograde flow in response to the normal flow rates and pressures that exist across the site in which the prosthesis is placed.
The foregoing problems are solved and a technical advance is achieved in an illustrative prosthesis having a sleeve which permits antegrade flow under a first pressure through the sleeve, and collapses in response to a second flow or pressure that is greater than the first flow or pressure.
In one aspect of the invention, the prosthesis comprises an anti-reflux esophageal prosthesis in which a sleeve extending from a tubular frame thereof inverts through the passage of the tubular frame and allows stomach gas or vomit to flow in a retrograde direction when the pressure in the stomach exceeds a given level. In the antegrade or downward position, the sleeve collapses and prevents the reflux of stomach gas and fluid from flowing through the esophagus and into the mouth of the patient. The collapsible sleeve functions as a one-way valve and allows the patient to ingest or pass liquid and food therethrough and into the stomach. In addition, the tubular frame of this advantageous anti-reflux esophageal prosthesis maintains the patency of the lower esophagus and sphincter particularly when a cancerous tumor impedes fluid flow through the esophagus.
In another advantageous aspect of the present invention, the tubular frame of the anti-reflux esophageal prosthesis includes a plurality of self-expanding zig-zag stents. The compressed stents along with the sleeve are positioned in an delivery catheter which is orally passed through the esophagus and lower sphincter. The prosthesis is then deployed from the delivery catheter with, for example, a dilator or pusher catheter that is inserted in the lumen of the delivery catheter. The deployed, self-expanding stents readily expand to engage the esophagus and lower sphincter and maintain them in a patent condition.
The self-expanding stents of the tubular frame are also advantageously flared at each end of the tubular frame to prevent antegrade and retrograde migration of the expanded prosthesis. To further prevent migration of the zig-zag stents with respect to each other, a filament is circumferentially positioned through closed eyelets at the bends of adjacent zig-zag stents. The filaments are also utilized advantageously to control the radial expansion and the flared configuration of the stents positioned at the ends of the tubular frame.
The pressure needed to collapse or invert the one-way valvular sleeve is a function of the sleeve material, its wall thickness and length extending from the distal end of the tubular frame. Depending on the anatomical size of the human or veterinary patient, the sleeve can extend from the end of the frame for a length in a range of from 0.0 to 20 cm, preferably in a range of 5 to 15 cm; and more preferably in length of approximately 10 cm in a human patient or 8 cm in a veterinary patient as experimentally derived therefor. The sleeve material also advantageously includes a material of polyurethane, silicone, polyamides, other urethanes or any biocompatible material that is flexible and acid resistant. The sleeve material can have an advantageous thickness of 0.005xe2x80x3 through 0.008xe2x80x3. This thickness is at the portion covering the frame itself. The sleeve extending from an end of the frame comprises a material having a thickness in a range of 0.0015xe2x80x3 to and including 0.004xe2x80x3 and preferably approximately 0.002xe2x80x3. Advantageously, the length of the sleeve is made long enough so that it can be readily shortened to accommodate individual anatomical situations.
In another aspect of the invention the collapsible sleeve is attached to a tubular drainage stent, such as a biliary stent, to advantageously prevent reflux of intestinal contents and the associated bacteria into the passage of the stent. These bacteria are known to promote the formation of biofilm which can lead to occlusion of the stent. With the stent placed in the biliary tree for maintaining patency of the bile or pancreatic duct and the Papilla of Vater, the sleeve extends down into the duodenum to provide a one-way valve for the flow of bile. When bile is not being secreted, the sleeve advantageously collapses to prevent backflow of material from the duodenum, a situation which might otherwise occur in a biliary stent without a closure means. Tubular drainage stents for placement in the ureters or urethra can include either a sleeve extending from one end to permit urine flow and prevent retrograde flow or pathogen migration toward the kidneys or bladder, or the sleeve may be located completely within the lumen of the drainage stent with one end of the sleeve being bonded or otherwise attached to the inner walls of the lumen.